时间: 2020-09-03 00:08:26 人气: 2278 评论: 0
在Android系统中有一个窗口的概念，我们所看到的所有界面都是窗口，由系统的WindowManagerService（WMS）管理着。App在没有悬浮窗权限下，不能添加系统级窗口，但却可以显示Toast。这说明Toast不在悬浮窗权限控制下，系统中某些机制保证了Toast的显示。
1、打开Toast源码，在调用Toast.show()后，Toast取出了系统服务NWS，与通知栏一样，Toast算是通知的一种。
/** * Show the view for the specified duration. */ public void show() { if (mNextView == null) { throw new RuntimeException("setView must have been called"); } INotificationManager service = getService(); String pkg = mContext.getOpPackageName(); TN tn = mTN; tn.mNextView = mNextView; try { service.enqueueToast(pkg, tn, mDuration); } catch (RemoteException e) { // Empty } }
其中TN是一个Binder对象，用于App与NMS间通信，对于NMS来说一个TN代表了一个Toast；mNextView是用于显示Toast内容的View，在使用Toast.makeText方法创建的Toast中，nNextView是一个包含TextView的LinearLayout。
/** * Make a standard toast to display using the specified looper. * If looper is null, Looper.myLooper() is used. * @hide */ public static Toast makeText(@NonNull Context context, @Nullable Looper looper, @NonNull CharSequence text, @Duration int duration) { Toast result = new Toast(context, looper); LayoutInflater inflate = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null); TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message); tv.setText(text); result.mNextView = v; result.mDuration = duration; return result; }
在show()中调用了NMS.enqueueToast()，相当于将Toast都集合到NMS中进行调度。当NMS调度到当次Toast时，则通过TN的Binder代理调用TN.show()方法。其中参数IBinder是一个窗口Token，用于添加窗口的鉴权。
/** * schedule handleShow into the right thread */ @Override public void show(IBinder windowToken) { if (localLOGV) Log.v(TAG, "SHOW: " + this); mHandler.obtainMessage(SHOW, windowToken).sendToTarget(); }
上述通过mHandler调度最终执行到TN.handleShow()方法，通过WMS.addView将mNextView添加到新的窗口中，并设置该窗口属性，达到Toast显示的目的。
public void handleShow(IBinder windowToken) { if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView + " mNextView=" + mNextView); // If a cancel/hide is pending - no need to show - at this point // the window token is already invalid and no need to do any work. if (mHandler.hasMessages(CANCEL) || mHandler.hasMessages(HIDE)) { return; } if (mView != mNextView) { // remove the old view if necessary handleHide(); mView = mNextView; Context context = mView.getContext().getApplicationContext(); String packageName = mView.getContext().getOpPackageName(); if (context == null) { context = mView.getContext(); } mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE); // We can resolve the Gravity here by using the Locale for getting // the layout direction final Configuration config = mView.getContext().getResources().getConfiguration(); final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection()); mParams.gravity = gravity; if ((gravity & Gravity.HORIZONTAL_GRAVITY_MASK) == Gravity.FILL_HORIZONTAL) { mParams.horizontalWeight = 1.0f; } if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == Gravity.FILL_VERTICAL) { mParams.verticalWeight = 1.0f; } mParams.x = mX; mParams.y = mY; mParams.verticalMargin = mVerticalMargin; mParams.horizontalMargin = mHorizontalMargin; mParams.packageName = packageName; mParams.hideTimeoutMilliseconds = mDuration == Toast.LENGTH_LONG ? LONG_DURATION_TIMEOUT : SHORT_DURATION_TIMEOUT; mParams.token = windowToken; if (mView.getParent() != null) { if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this); mWM.removeView(mView); } if (localLOGV) Log.v(TAG, "ADD! " + mView + " in " + this); // Since the notification manager service cancels the token right // after it notifies us to cancel the toast there is an inherent // race and we may attempt to add a window after the token has been // invalidated. Let us hedge against that. try { mWM.addView(mView, mParams); trySendAccessibilityEvent(); } catch (WindowManager.BadTokenException e) { /* ignore */ } } }
Toast时长到达后，由NMS调度并调用TN.hide()
/** * schedule handleHide into the right thread */ @Override public void hide() { if (localLOGV) Log.v(TAG, "HIDE: " + this); mHandler.obtainMessage(HIDE).sendToTarget(); }
最终也是通过WMS.removeView()达到Toast消失的目的。
public void handleHide() { if (localLOGV) Log.v(TAG, "HANDLE HIDE: " + this + " mView=" + mView); if (mView != null) { // note: checking parent() just to make sure the view has // been added... i have seen cases where we get here when // the view isn't yet added, so let's try not to crash. if (mView.getParent() != null) { if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this); mWM.removeViewImmediate(mView); } // Now that we've removed the view it's safe for the server to release // the resources. try { getService().finishToken(mPackageName, this); } catch (RemoteException e) { } mView = null; } }
我们再看Toast与一般悬浮窗窗口的区别：Toast的窗口类型是TYPE_TOAST，其他使用悬浮窗使用的时TYPE_PHONE/TYPE_SYSTEM_ALTER。在系统侧WMS中针对不同的窗口类型有不同的限制：由源码中可以看到，在处理TYPE_TOAST类型的窗口时直接跳过了悬浮窗权限检查（在Android O及以上则需要一个有NMS分配的token），而TYPE_PHONE/TYPE_SYSYTEM_ALTER则需要权限检查。
@Override
public int checkAddPermission(WindowManager.LayoutParams attrs, int[] outAppOp) {
final int type = attrs.type;
final boolean isRoundedCornerOverlay =
(attrs.privateFlags & PRIVATE_FLAG_IS_ROUNDED_CORNERS_OVERLAY) != 0;
if (isRoundedCornerOverlay && mContext.checkCallingOrSelfPermission(INTERNAL_SYSTEM_WINDOW)
!= PERMISSION_GRANTED) {
return ADD_PERMISSION_DENIED;
}
outAppOp[0] = AppOpsManager.OP_NONE;
if (!((type >= FIRST_APPLICATION_WINDOW && type <= LAST_APPLICATION_WINDOW)
|| (type >= FIRST_SUB_WINDOW && type <= LAST_SUB_WINDOW)
|| (type >= FIRST_SYSTEM_WINDOW && type <= LAST_SYSTEM_WINDOW))) {
return WindowManagerGlobal.ADD_INVALID_TYPE;
}
if (type < FIRST_SYSTEM_WINDOW || type > LAST_SYSTEM_WINDOW) {
// Window manager will make sure these are okay.
return ADD_OKAY;
}
if (!isSystemAlertWindowType(type)) {
switch (type) {
case TYPE_TOAST:
// Only apps that target older than O SDK can add window without a token, after
// that we require a token so apps cannot add toasts directly as the token is
// added by the notification system.
// Window manager does the checking for this.
outAppOp[0] = OP_TOAST_WINDOW;
return ADD_OKAY;
case TYPE_DREAM:
case TYPE_INPUT_METHOD:
case TYPE_WALLPAPER:
case TYPE_PRESENTATION:
